That's good that you tested the pressures. The readings are hard to comment on because pressure is a function of temperature. Typically once you are at operating temp, the system should hold pressure as rated on the radiator cap for at least 30 min. It will decrease over time as the system cools. So in hot summer weather, the pressure drop will be less and over a longer period o time than in the winter. If a combustion leak, it will get really high, causing the overflow tank to fill, and after reaching operating temp, shutting off the engine, if you were to open the rad cap, you would have a large amount of escaping coolant/pressure. Also, you upper/lower rad hoses would be quite firm after a few minutes post shut down.

Unfortunately, none of this can be tested with the system open as you have it now.

The only other suggestions I can offer is to thoroughly clean your radiator, making sure no leaves or debris are in between the condensor if equipped and radiator. I would also recommend a citric acid flush of the radiator itself to make sure it is not coated with oil internally restricting heat transfer.

The odd thing is your temperature differential in/out of the rad. Seems like it's functioning well, which would also indicate the pump is flowing. Possible restriction between the pump and head, maybe reverse flush between the two if disassembled.

I'm out of ideas on this one. Best of luck